defmodule Symbiont.Telepathy.JMAP do
  @moduledoc """
  JMAP client GenServer for Fastmail (RFC 8620/8621).

  Discovers the JMAP session, then periodically polls for new inbound emails.
  New emails are stored in the MessageStore. Also provides send_email/3 for
  outbound mail.

  Uses :httpc from :inets (no external HTTP dependency).
  """
  use GenServer
  require Logger

  @jmap_session_url "https://api.fastmail.com/jmap/session"
  @core_cap "urn:ietf:params:jmap:core"
  @mail_cap "urn:ietf:params:jmap:mail"
  @submit_cap "urn:ietf:params:jmap:submission"

  @default_poll_interval_ms 60_000
  @config_path "/data/telepathy/config.json"

  defstruct [
    :token,
    :api_url,
    :account_id,
    :identity_id,
    :from_email,
    :drafts_id,
    :inbox_id,
    :poll_interval_ms,
    seen_ids: MapSet.new()
  ]

  # -- Client API --

  def start_link(opts) do
    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
  end

  def send_email(to, subject, body) do
    GenServer.call(__MODULE__, {:send_email, to, subject, body}, 30_000)
  end

  def session_info do
    GenServer.call(__MODULE__, :session_info)
  end

  def fetch_now do
    send(__MODULE__, :poll)
    :ok
  end

  # -- Server --

  @impl true
  def init(opts) do
    poll_ms = Keyword.get(opts, :poll_interval_ms, @default_poll_interval_ms)
    token = load_token()

    state = %__MODULE__{
      token: token,
      poll_interval_ms: poll_ms
    }

    send(self(), :discover_session)
    {:ok, state}
  end

  @impl true
  def handle_info(:discover_session, state) do
    case discover_session(state.token) do
      {:ok, session} ->
        Logger.info("Telepathy JMAP session discovered: account=#{session.account_id}")

        new_state = %{
          state
          | api_url: session.api_url,
            account_id: session.account_id,
            identity_id: session.identity_id,
            from_email: session.from_email,
            drafts_id: session.drafts_id,
            inbox_id: session.inbox_id
        }

        seen = seed_seen_ids()
        schedule_poll(new_state.poll_interval_ms)
        {:noreply, %{new_state | seen_ids: seen}}

      {:error, reason} ->
        Logger.error("Telepathy JMAP session discovery failed: #{inspect(reason)}")
        Process.send_after(self(), :discover_session, 10_000)
        {:noreply, state}
    end
  end

  @impl true
  def handle_info(:poll, %{api_url: nil} = state) do
    schedule_poll(state.poll_interval_ms)
    {:noreply, state}
  end

  @impl true
  def handle_info(:poll, state) do
    new_state =
      case fetch_inbox_emails(state) do
        {:ok, emails} ->
          {new_count, updated_seen} = store_new_emails(emails, state.seen_ids)

          if new_count > 0,
            do: Logger.info("Telepathy: fetched #{new_count} new email(s)")

          %{state | seen_ids: updated_seen}

        {:error, reason} ->
          Logger.warning("Telepathy JMAP poll failed: #{inspect(reason)}")
          state
      end

    schedule_poll(new_state.poll_interval_ms)
    {:noreply, new_state}
  end

  @impl true
  def handle_call({:send_email, to, subject, body}, _from, state) do
    result = do_send_email(state, to, subject, body)
    {:reply, result, state}
  end

  @impl true
  def handle_call(:session_info, _from, state) do
    info = %{
      api_url: state.api_url,
      account_id: state.account_id,
      identity_id: state.identity_id,
      from_email: state.from_email,
      inbox_id: state.inbox_id,
      seen_count: MapSet.size(state.seen_ids)
    }

    {:reply, info, state}
  end

  # -- Private: Session Discovery --

  defp discover_session(token) do
    with {:ok, session_resp} <- jmap_get(@jmap_session_url, token),
         api_url <- session_resp["apiUrl"],
         account_id <- get_in(session_resp, ["primaryAccounts", @mail_cap]),
         {:ok, details} <- fetch_identity_and_mailboxes(api_url, account_id, token) do
      {:ok, Map.merge(%{api_url: api_url, account_id: account_id}, details)}
    end
  end

  defp fetch_identity_and_mailboxes(api_url, account_id, token) do
    method_calls = [
      ["Identity/get", %{"accountId" => account_id, "ids" => nil}, "id0"],
      ["Mailbox/get", %{"accountId" => account_id, "ids" => nil}, "mb0"]
    ]

    case jmap_call(api_url, token, method_calls) do
      {:ok, responses} ->
        identity = extract_identity(responses)
        {drafts_id, inbox_id} = extract_mailbox_ids(responses)

        {:ok,
         %{
           identity_id: identity[:id],
           from_email: identity[:email] || "mdwyer@michaelmdwyer.com",
           drafts_id: drafts_id,
           inbox_id: inbox_id
         }}

      error ->
        error
    end
  end

  defp extract_identity(responses) do
    target = "mdwyer@michaelmdwyer.com"

    Enum.find_value(responses, %{id: nil, email: nil}, fn
      ["Identity/get", data, _] ->
        identities = data["list"] || []

        match =
          Enum.find(identities, fn i ->
            String.downcase(i["email"] || "") == target
          end) || List.first(identities)

        if match, do: %{id: match["id"], email: match["email"]}, else: %{id: nil, email: nil}

      _ ->
        nil
    end)
  end

  defp extract_mailbox_ids(responses) do
    Enum.find_value(responses, {nil, nil}, fn
      ["Mailbox/get", data, _] ->
        mailboxes = data["list"] || []
        drafts = Enum.find(mailboxes, &(&1["role"] == "drafts"))
        inbox = Enum.find(mailboxes, &(&1["role"] == "inbox"))
        {drafts && drafts["id"], inbox && inbox["id"]}

      _ ->
        nil
    end)
  end

  # -- Private: Fetch Loop --

  defp fetch_inbox_emails(state) do
    method_calls = [
      [
        "Email/query",
        %{
          "accountId" => state.account_id,
          "filter" => %{"inMailbox" => state.inbox_id},
          "sort" => [%{"property" => "receivedAt", "isAscending" => false}],
          "limit" => 20
        },
        "q0"
      ],
      [
        "Email/get",
        %{
          "accountId" => state.account_id,
          "#ids" => %{
            "resultOf" => "q0",
            "name" => "Email/query",
            "path" => "/ids"
          },
          "properties" => [
            "id",
            "from",
            "to",
            "subject",
            "receivedAt",
            "textBody",
            "bodyValues",
            "preview"
          ],
          "fetchTextBodyValues" => true
        },
        "g0"
      ]
    ]

    case jmap_call(state.api_url, state.token, method_calls) do
      {:ok, responses} ->
        emails =
          Enum.find_value(responses, [], fn
            ["Email/get", data, _] -> data["list"] || []
            _ -> nil
          end) || []

        {:ok, emails}

      error ->
        error
    end
  end

  defp store_new_emails(emails, seen_ids) do
    new_emails = Enum.reject(emails, &MapSet.member?(seen_ids, &1["id"]))

    Enum.each(new_emails, fn email ->
      body = extract_body(email)
      from = extract_from(email)
      subject = email["subject"] || "(no subject)"

      msg = %{
        "source" => "email-in",
        "subject" => subject,
        "content" => "[From: #{from}]\n#{body}",
        "jmap_id" => email["id"],
        "received_at" => email["receivedAt"]
      }

      Symbiont.Telepathy.MessageStore.store(msg)
    end)

    new_seen =
      new_emails
      |> Enum.map(& &1["id"])
      |> Enum.reduce(seen_ids, &MapSet.put(&2, &1))

    {length(new_emails), new_seen}
  end

  defp extract_body(email) do
    body_values = email["bodyValues"] || %{}
    text_body = email["textBody"] || []

    case text_body do
      [%{"partId" => part_id} | _] ->
        get_in(body_values, [part_id, "value"]) || email["preview"] || ""

      _ ->
        email["preview"] || ""
    end
  end

  defp extract_from(email) do
    case email["from"] do
      [%{"name" => name, "email" => addr} | _] when is_binary(name) and name != "" ->
        "#{name} <#{addr}>"

      [%{"email" => addr} | _] ->
        addr

      _ ->
        "unknown"
    end
  end

  # -- Private: Send Email --

  defp do_send_email(state, to, subject, body) do
    method_calls = [
      [
        "Email/set",
        %{
          "accountId" => state.account_id,
          "create" => %{
            "e1" => %{
              "mailboxIds" => %{state.drafts_id => true},
              "from" => [%{"name" => "Muse", "email" => state.from_email}],
              "to" => [%{"email" => to}],
              "subject" => subject,
              "replyTo" => [%{"name" => "Muse", "email" => "muse@hydrascale.net"}],
              "keywords" => %{"$draft" => true},
              "bodyStructure" => %{"type" => "text/plain", "partId" => "body"},
              "bodyValues" => %{"body" => %{"value" => body, "charset" => "utf-8"}}
            }
          }
        },
        "create-email"
      ],
      [
        "EmailSubmission/set",
        %{
          "accountId" => state.account_id,
          "create" => %{
            "s1" => %{
              "identityId" => state.identity_id,
              "emailId" => "#e1"
            }
          }
        },
        "send"
      ]
    ]

    case jmap_call(state.api_url, state.token, method_calls) do
      {:ok, responses} ->
        parse_send_response(responses)

      {:error, reason} ->
        {:error, reason}
    end
  end

  defp parse_send_response(responses) do
    Enum.reduce(responses, %{email_id: nil, sent: false, errors: []}, fn
      ["Email/set", data, _], acc ->
        case get_in(data, ["created", "e1", "id"]) do
          nil ->
            error = get_in(data, ["notCreated", "e1"])
            %{acc | errors: ["Email create: #{inspect(error)}" | acc.errors]}

          id ->
            %{acc | email_id: id}
        end

      ["EmailSubmission/set", data, _], acc ->
        if get_in(data, ["created", "s1"]) do
          %{acc | sent: true}
        else
          error = get_in(data, ["notCreated", "s1"])
          %{acc | errors: ["Submission: #{inspect(error)}" | acc.errors]}
        end

      _, acc ->
        acc
    end)
    |> then(fn
      %{sent: true, email_id: id} -> {:ok, id}
      %{errors: errors} -> {:error, Enum.join(errors, "; ")}
    end)
  end

  # -- Private: HTTP Helpers (using :httpc) --

  defp jmap_get(url, token) do
    headers = [{~c"Authorization", ~c"Bearer #{token}"}]

    case :httpc.request(:get, {String.to_charlist(url), headers}, [{:timeout, 15_000}], []) do
      {:ok, {{_, 200, _}, _, body}} ->
        Jason.decode(IO.iodata_to_binary(body))

      {:ok, {{_, status, _}, _, body}} ->
        {:error, {:http, status, IO.iodata_to_binary(body)}}

      {:error, reason} ->
        {:error, reason}
    end
  end

  defp jmap_call(api_url, token, method_calls) do
    payload =
      Jason.encode!(%{
        "using" => [@core_cap, @mail_cap, @submit_cap],
        "methodCalls" => method_calls
      })

    headers = [
      {~c"Authorization", ~c"Bearer #{token}"},
      {~c"Content-Type", ~c"application/json"}
    ]

    case :httpc.request(
           :post,
           {String.to_charlist(api_url), headers, ~c"application/json", payload},
           [{:timeout, 30_000}],
           []
         ) do
      {:ok, {{_, 200, _}, _, body}} ->
        case Jason.decode(IO.iodata_to_binary(body)) do
          {:ok, %{"methodResponses" => responses}} -> {:ok, responses}
          {:ok, other} -> {:error, {:unexpected_response, other}}
          {:error, _} = err -> err
        end

      {:ok, {{_, status, _}, _, body}} ->
        {:error, {:http, status, IO.iodata_to_binary(body)}}

      {:error, reason} ->
        {:error, reason}
    end
  end

  defp schedule_poll(interval_ms) do
    Process.send_after(self(), :poll, interval_ms)
  end

  defp load_token do
    case System.get_env("FASTMAIL_API_TOKEN") do
      nil -> load_token_from_config()
      "" -> load_token_from_config()
      token -> token
    end
  end

  defp load_token_from_config do
    case File.read(@config_path) do
      {:ok, content} ->
        case Jason.decode(content) do
          {:ok, %{"fastmail_token" => token}}
          when is_binary(token) and token != "" and token != "PLACEHOLDER" ->
            token

          _ ->
            raise "No valid fastmail_token in #{@config_path}"
        end

      {:error, _} ->
        raise "Cannot read #{@config_path} — set FASTMAIL_API_TOKEN env var"
    end
  end

  defp seed_seen_ids do
    case Symbiont.Telepathy.MessageStore.list(limit: 10_000) do
      messages when is_list(messages) ->
        messages
        |> Enum.map(& &1["jmap_id"])
        |> Enum.reject(&is_nil/1)
        |> MapSet.new()

      _ ->
        MapSet.new()
    end
  end
end